5.4.0 General

24.2293GPPIP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Release 18Stage 3TS

Where the S-CSCF provides emergency call support, the procedures of subclause 5.4.8 shall be applied first.

Upon

1) a third-party registration due to initial registration on behalf of a served public user identity; or

2) a trigger to an AS for an unregistered public user identity and there is no IP address of that AS associated with that public user identity stored;

the S-CSCF shall store the IP address of the AS and associate the IP address with the public user identity and the AS SIP URI along with all URI parameters.

When sending a failure response to any received request, depending on operator policy, the S-CSCF may insert a Response-Source header field with an "fe" header field parameter constructed with the URN namespace "urn:3gpp:fe", the fe-id part of the URN set to "s-cscf" and optionally an appropriate fe-param part of the URN set in accordance with subclause 7.2.17. A S-CSCF when sending a failure response will add in the URN the "side" header field parameter set to:

– "orig" for a UE-originating case; and

– "term" for a UE-terminating case.